Field of the Invention
The present invention relates to a brake disc and, more particularly, to a brake disc manufacturing by combining different kinds of materials.
Description of Related Art
In general, a brake disc applied to vehicles includes a hub part connected to a drive shaft and a disc part contacting a friction material.
The disc part substantially generates frictional force and thus converts kinetic energy into thermal energy and thus requires high heat resistance and abrasion resistance and, for the present purpose, the disc part may be formed of cast iron.
However, cast iron is based on iron and thus has a high density and is heavy.
Therefore, to reduce the weight of the brake disc, weight reduction technology, in which a disc part directly generating friction is formed of cast iron and a hub part to connect the disc part to a drive shaft is formed of an aluminum alloy, has been developed.
However, since it is difficult to execute surface junction between cast iron and an aluminum alloy by welding, a method of structurally combining a disc part and a hub part formed of cast iron and the aluminum alloy with each other using protrusions and recesses has been used.
That is, a disc part formed of cast iron is manufactured to have a ring shape, a hub part is formed by injecting molten aluminum to surround connection parts protruding from the inner circumferential surface of the disc part and, thereby, the disc part and the hub part formed of different kinds of materials may be combined integrally with each other.
FIG. 1 and FIG. 2 illustrate a conventional structure of combining a disc part and a hub part with each other. As shown in FIG. 1 and FIG. 2, a disc part 10 and a hub part 20 are combined into one body to be rotatable by inserting connection parts 30 protruding from the inside circumferential surface of the disc part 10 into recesses 21 of the hub part 20.
Here, the connection part 30 is divided into a curved section 31 extending from the inside circumferential surface of the disc part 10, a parallel section 32 extending from the end of the curved section 31, and an inclined section 33 extending from the end of the parallel section 32.
The curved section 31 and the inclined section 32 are configured wherein the widths thereof gradually decrease in a direction toward the hub part 20, and the parallel section 32 has a uniform width and thus contact the inside surface of the recess 21 of the hub part 20.
When the disc part 10 and the hub part 20 are connected through such a structure, combination between the disc part 10 and the hub part 20 may be stably maintained although thermal expansion and thermal stress occurs due to frictional heat during braking.
However, cast iron and an aluminum alloy have different coefficients of thermal expansion and, when heat generated from the disc part 10 is transmitted to the hub part 20 and thus the disc part 10 momentarily contracts and the hub part 20 expands, stick-slip occurs due to stress between the disc part 10 and the hub part 20, thus generating noise.
Since stick-slip is increased in proportion to exciting force determined by stress (N)×difference of coefficients of friction {static friction coefficient (μs)−dynamic friction coefficient (μk)} and thereby noise is increased, to reduce such noise, stress between the disc part and the hub part should be reduced.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.